The present description relates to a method of controlling an internal combustion engine, and more particularly relates to a method of feedback controlling an air fuel ratio of air fuel mixture supplied to an internal combustion engine using a heated exhaust gas oxygen sensor.
There is known and presented, for example in U.S. Pat. No. 6,848,439, an exhaust gas oxygen sensor arranged in an exhaust passage between an internal combustion engine and a catalytic converter. The sensor is capable of outputting a signal that corresponds linearly to the oxygen concentration in the exhaust gases. The '439 patent also shows a method of using the sensor output for feedback controlling an air-fuel mixture to an internal combustion engine. The exhaust gas oxygen sensor outputs a linear signal when its temperature is within a higher operative temperature range, between 700-800° C. for example. On the other hand, the sensor outputs a non-linear signal around the stoichiometric air-fuel ratio at a lower operative temperature range, between 300-400° C. for example. The exhaust gas oxygen sensor is provided with a heater, which may be used to heat the sensor temperature to the operative range.
When the exhaust gas oxygen sensor is cooled down after an engine stop and an internal combustion engine is started again, a water content of the exhaust gas or combusted gas may be partly condensed by contacting the sensor surface. If the heater is then used to heat the exhaust gas oxygen sensor, the condensed water may cause the sensor output to degrade. The '439 patent describes a method to avoid such degradation by choosing the lower temperature range as its target temperature. The '439 patent also describes using the sensor at lower operating temperatures to provide feedback control of engine air fuel mixtures around the stoichiometric air fuel ratio within a predetermined time period after an engine start.
However, it is possible under certain circumstances to increase the amount of water in the exhaust gas that condenses on the sensor surface. For example, when hydrogen is used as a fuel instead of fossil fuels, such as gasoline, combustion of hydrogen may create more water in the exhaust gas because hydrogen readily combines with air to produce water. As the amount of the condensed water increases, it may make it difficult to heat the sensor after an engine start, even to the lower target temperature. Further, since combusted hydrogen exhibits lower exhaust gas temperatures, the time period that condensation occurs in the exhaust system can be increased when compared to combusted fossil fuels. The condensation may make it difficult to precisely feedback control the engine air-fuel ratio based on feedback from the sensor output. Consequently, engine emissions and fuel economy may be degraded when exhaust gases condensate into water in the exhaust system.
Therefore, there is a need to improve the prior art method of feedback controlling an air-fuel ratio using a heated exhaust gas oxygen sensor.